Overcurrent protection in industrial enclosure with VFDs

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paulbr

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Hello.
I am at design stage and would like to get some input.
There will be industrial enclosure with two VFDs: 150Hp and 50Hp and some 24VDC components. Each VFD controls its respective motor. Here is single line sketch.
My question is do I even need CB1? Can Main Breaker CB100, which is 500A, serve as feeder OCPD and BCPD for 150Hp motor at the same time? From instructions from VFD manufacturer max. size of protection circuit breaker is 550A. Need to make it right. This electrical enclosure will have UL label.
Thanks in advance for advice.
PaulBr

single line.jpg
 
No reason you can't. It's a common practice.

You might want to consider if there is ever a case where you might want to run the smaller motor while the larger one is locked out.
 
If BOTH motors must run at the same time, then you are correct that the 500A breaker ahead of both drives, interlocked with the door, will suffice as the main disconnect and the OCPD of the larger drive. You WILL still need the smaller breaker for the smaller drive, but I think you know that.

UL will be OK with that arrangement too by the way, so long as you are following the manufacturers instructions and UL listing information.
 
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